Are Democratic Presidents Better for Babies?

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But when the researchers used statistical methods to focus on short-term changes during this time period, they found that infant mortality rates were about 3 percent higher during years in which a Republican was president, compared with the years in which a Democrat was president. [The 5 Strangest Presidential Elections in US History]

The findings held even after the researchers took into account factors that might affect infant mortality, such as unemployment rates, smoking rates, abortion rates and measures of national education and income level. And the researchers did not consider the first year of any president's term, they said, because a president's policies would not be expected to affect mortality in the first year of his presidency.

The researchers acknowledged that their findings could be accidental: infant mortality and the president's party may be completely unrelated, and instead, what seems to be a link between the president's political party and infant mortality could actually be due to other factors that shift back and forth over four to eight years.

However, the researchers said they were "struck by the consistency of the association we have uncovered," according to the study published online in the International Journal of Epidemiology on Dec. 30, 2013.

If the findings are true, "the association could arise because of conditions existing for mothers and infants during Democratic vs Republican administrations," the researchers, from the University of Michigan, wrote in the study.

A political party in power may influence infant mortality rates because its ideology may promote the interests or well-being of different groups of people in the U.S., the researchers said in their study.

For example, "whether a government advocates austerity measures, or increasing social welfare protections as the response to economic crisis may reflect such ideological differences and influence mortality rates," they wrote.

Still, they noted that many factors influence population health, and that the president's party doesn't always affect legislation that is passed. Future research is needed to determine the reason for the link, they said.

Some experts were critical of the findings. In an editorial published after the study in the same journal, Ralph Catalano, a professor of public health at the University of California, Berkeley, said the statistical methods the researchers used in the study were not appropriate for the type of data they were analyzing. He said that analyzing the data a different way, using a conventional method that most in the field would use, showed no association between the U.S. president's party and infant mortality. (The method involved, in part, using infant mortality data from Canada, a population in which one would not expect to find the same link.)

"I, even as a Democrat who has served in political office, am not buying [the findings], and I doubt many serious epidemiologists will," Catalano wrote. (Catalano was a city councilman in Irvine, Calif. in the 1980s.)